Organic light emitting diode display and method for manufacturing the same

ABSTRACT

An organic light emitting device including a first pixel, a second pixel and a third pixel displaying different colors from each other according to the present invention, the organic light emitting device includes a reflecting electrode and a translucent member forming a micro-cavity along with the reflecting electrode, wherein a optical path length is an interval between the reflecting electrode and the translucent member, and wherein the light path lengths of at least two pixels among the first pixel, the second pixel and the third pixel are the same.

This application is a divisional of U.S. application Ser. No.12/112,684, filed on Apr. 30, 2008, which claims priority to KoreanPatent Application No. 10-2007-0112255, filed on Nov. 5, 2008, and allthe benefits accruing therefrom under 35 U.S.C. §119, the contents ofwhich in its entirety are herein incorporated by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to an organic light emitting diode displayand a manufacturing method thereof.

(b) Description of the Related Art

Recent trends toward lightweight and thin personal computers andtelevisions sets have increased the desire for lightweight and thindisplay devices associated therewith. Flat panel displays, such as aliquid crystal display (“LCD”) satisfying such requirements, are beingsubstituted for conventional cathode ray tubes (“CRTs”).

However, because the LCD is a passive display device, an additionalback-light as a light source is needed. In addition, the LCD hasadditional drawbacks such as a slow response time and a narrow viewingangle.

Among the flat panel displays, an organic light emitting diode (“OLED”)display has recently been the most promising as a display device forsolving these drawbacks associated with other flat panel displays.

The OLED display includes two electrodes and an organic light emittinglayer interposed between the two electrodes. One of the two electrodesinjects holes and the other electrode injects electrons into the organiclight emitting layer. The injected electrons and holes are recombined toform excitons, which emit light as release energy.

Because the OLED display is a self-emissive display device, anadditional light source is not necessary such that the OLED display haslower power consumption, as well as a high response speed, wide viewingangle and high contrast ratio.

On the other hand, the OLED display includes a plurality of pixels suchas red pixels, blue pixels and green pixels, and images of full colorsmay be displayed by selectively combining these pixels.

However, the OLED display has different light emitting efficiencyaccording to light emitting materials. That is, a material having lowlight emitting efficiency among red, green and blue cannot represent thecolors of a desired color coordinate, and it is also difficult todisplay a desired white color due to the material having the low lightemitting efficiency in the case of emitting white color by combiningred, green and blue.

To improve the light emitting efficiency, a micro-cavity may be used.

In a micro-cavity, light is repeatedly reflected between a reflectionlayer and a translucent layer in which both layers are separated by apredetermined distance (e.g., an optical path length) such that a stronginterference effect is generated in the light. Accordingly, light of aspecific wavelength is constructive, and light of remaining wavelengthsis destructive.

Accordingly, the luminance and the color reproducibility may besimultaneously improved at the front side.

However, to represent full colors by using the micro-cavity, the redpixel, green pixel and blue pixel must have different optical pathlengths corresponding to the wavelengths of each pixel. To form thedifferent optical path lengths for each pixel, additional processingsteps are required to form the micro-cavities for each pixel arerequired, thus increasing the number of total manufacturing processes.

BRIEF SUMMARY OF THE INVENTION

An aspect, feature and advantage provided by exemplary embodiments ofthe present invention include simplification of the processes forforming the micro-cavity as well as to improvement of the luminance andcolor reproducibility by using the micro-cavity.

An OLED display according to an exemplary embodiment of the presentinvention includes a first pixel, a second pixel, and a third pixeldisplaying different colors from each other, and each pixel includes areflecting electrode and a translucent member forming a micro-cavityalong with the reflecting electrode. An optical path length is a gapbetween the reflecting electrode and the translucent member, and theoptical path lengths of at least two pixels among the first pixel, thesecond pixel and the third pixel are the same.

The OLED display may further include a transparent member disposedbetween the reflecting electrode and the translucent member, and thetransparent member may be formed in a portion of at least one pixelamong the first pixel, the second pixel and the third pixel.

The translucent member may include silver or aluminum, and thetransparent member may include ITO or IZO.

The optical path lengths of the first pixel and the second pixel may bethe same, and the transparent member may be formed in the third pixeland not in the first pixel and the second pixel.

The first pixel may be a red pixel, the second pixel may be a bluepixel, and the third pixel may be a green pixel.

The optical path lengths L₁ of the first pixel and the second pixel maysatisfy L₁≈mλ₁/2≈(m+1)λ₂/2 and the optical path length L₂ of the thirdpixel may satisfy L₂≈(m+1)λ₃/2, where m is a natural number, λ₁ is awavelength of the red region, λ₂ is a wavelength of the blue region, andλ₃ is a wavelength of the green region.

The optical path lengths of the first pixel and the second pixel may bethe same, and the transparent member may be formed in the first pixeland the second pixel and not in the third pixel.

The first pixel may be a green pixel, the second pixel may be a bluepixel, and the third pixel may be a red pixel.

The optical path length L₂ of the third pixel may satisfy L₂≈mλ₃/2 andthe optical path length L₁ of the first pixel and the second pixel maysatisfy L₁≈(m+1)λ₁/2≈(m+2)λ₂/2, where m is a natural number, λ₁ is awavelength of the green region, λ₂ is a wavelength of the blue region,and λ₃ is a wavelength of the red region.

The OLED display may further include a transparent electrode formedunder the translucent member.

The translucent member may include a plurality of layers, wherein thelayers include a first layer and a second layer which are alternatelydeposited and have different refractive indexes, and at least one layeramong the plurality of layers may be formed only in some pixels amongthe first pixel, the second pixel and the third pixel.

The optical path lengths of the first pixel and the second pixel may bethe same, and the at least one layer may be formed in the third pixeland not in the first pixel and the second pixel.

The first pixel may be the red pixel, the second pixel may be the bluepixel, and the third pixel may be the green pixel.

The optical path lengths L₁ of the first pixel and the second pixel maysatisfy L₁≈mλ₁/2≈(m+1)λ₂/2 and the optical path length L₂ of the thirdpixel satisfies L₂≈(m+1)λ₃/2, where m is a natural number, λ₁ is awavelength of the red region, λ₂ is a wavelength of the blue region, andλ₃ is a wavelength of the green region.

The optical path lengths of the first pixel and the second pixel may bethe same, and the at least one layer may be formed in the first pixeland the second pixel and not in the third pixel.

The first pixel may be the red pixel, the second pixel may be the bluepixel, and the third pixel may be the green pixel.

The optical path lengths L₁ of the first pixel and the second pixel maysatisfy L₁≈mλ₁/2≈(m+1)λ₂/2 and the optical path length L₂ of the thirdpixel may satisfy L₂≈mλ₃/2, where m is a natural number, λ₁ is awavelength of the red region, λ₂ is a wavelength of the blue region, andλ₃ is a wavelength of the green region.

The OLED display may further include a white pixel, and the translucentmember may be absent in the white pixel.

The OLED display may further include a thin film transistor, and apassivation layer formed on the thin film transistor, and thepassivation layer film may be absent in the white pixel.

The first pixel, the second pixel, and the third pixel may respectivelyinclude a corresponding color filter.

The OLED display may further include an emission member disposed betweenthe reflecting electrode and the translucent member, the emission membermay include a plurality of sub-emission layers emitting light ofdifferent wavelengths, and the emission member emits white light bycombining the light of the different wavelengths.

A method of manufacturing an OLED display including a plurality ofpixels displaying different colors from each other according to thepresent invention includes forming a translucent member, forming areflecting electrode, depositing a transparent conductive layer betweenthe translucent member and the reflecting electrode, and photo-etchingthe transparent conductive layer, wherein the transparent conductivelayer is maintained in some of the pixels and is removed in remainingpixels by the photo-etching.

A method of manufacturing an OLED display including a plurality ofpixels displaying different colors from each other according to anotherexemplary embodiment of the present invention includes forming areflecting electrode, forming an emission member under or on thereflecting electrode, forming a plurality of translucent layers whereina first layer and a second layer having different refractive indexes arealternately deposited to form the translucent layers, and photo-etchinga portion of the layers among the plurality of translucent layers,wherein the translucent layers are maintained in some pixels and areremoved in remaining pixels by the photo-etching.

The first layer may be made of a silicon nitride layer and the secondlayer may be made of a silicon oxide layer, the silicon nitride layermay be etched by using CF₄ and O₂, and the silicon oxide layer may beetched by using C₄F₈ and H₂.

The OLED display may further include a white pixel of the plurality ofpixels, and before forming the translucent layer, the method may furtherinclude forming a passivation layer and removing the passivation layerin the white pixel.

In an exemplary embodiment of the present invention, the colorreproducibility and luminance may be improved by using the micro-cavity.Further, at least two pixels among the plurality of pixels displayingthe different colors from each other have the same optical path lengthssuch that the number of processes for forming the different optical pathlengths for each pixel may be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an equivalent circuit schematic diagram of an OLED displayaccording to an exemplary embodiment of the present invention;

FIG. 2 is a schematic diagram showing an arrangement of a plurality ofpixels in the OLED display according to an exemplary embodiment of thepresent invention;

FIG. 3 is a cross-sectional view showing four neighboring pixels in theOLED display shown in FIG. 2;

FIG. 4 is a cross-sectional view showing an OLED display according toanother exemplary embodiment of the present invention;

FIG. 5 is a cross-sectional view showing an OLED display according toanother exemplary embodiment of the present invention;

FIG. 6 and FIG. 7 are cross-sectional views showing an OLED display,respectively, according to alternative exemplary embodiments of thepresent invention;

FIG. 8 is a graph showing red, green, and blue light spectrums and awhite light spectrum in the OLED display according to the presentexemplary embodiment; and

FIG. 9 is a graph showing an increased and decreased ratio of theintensity of the light spectrum by the micro-cavity in the graph shownin FIG. 8 compared with the intensity of a white light spectrum in thepredetermined wavelength.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described more fully hereinafter with reference to theaccompanying drawings, in which exemplary embodiments of the inventionare shown. The present invention may, however, be embodied in manydifferent forms and should not be construed as being limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likereference numerals refer to like elements throughout.

It will be understood that when an element or layer is referred to asbeing “on”, “connected to” or “coupled to” another element or layer, itcan be directly on, connected or coupled to the other element or layeror intervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on,” “directly connected to”or “directly coupled to” another element or layer, there are nointervening elements or layers present. Like numbers refer to likeelements throughout. As used herein, the term “and/or” includes any andall combinations of one or more of the associated listed items.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, components, regions, layersand/or sections, these elements, components, regions, layers and/orsections should not be limited by these terms. These terms are only usedto distinguish one element, component, region, layer or section fromanother region, layer or section. Thus, a first element, component,region, layer or section discussed below could be termed a secondelement, component, region, layer or section without departing from theteachings of the present invention.

Spatially relative terms, such as “beneath”, “below”, “lower”, “above”,“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms, “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “includes”and/or “including”, when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Hereinafter, the present invention will be explained in detail withreference to the accompanying drawings.

Now, an OLED display according to an exemplary embodiment of the presentinvention will be described in further detail with reference to FIG. 1.

FIG. 1 is an equivalent circuit schematic diagram of an OLED displayaccording to an exemplary embodiment of the present invention.

Referring to FIG. 1, the OLED display according to the present exemplaryembodiment includes a plurality of signal lines 121, 171 and 172, and aplurality of pixels PX connected thereto and arranged substantially in amatrix.

The signal lines include a plurality of gate lines 121 for transmittinggate signals (or scanning signals), a plurality of data lines 171 fortransmitting data signals, and a plurality of driving voltage lines 172for transmitting a driving voltage. The gate lines 121 extendsubstantially in a row direction and substantially parallel to eachother, and the data lines 171 and the driving voltage lines 172 extendsubstantially in a column direction and substantially parallel to eachother, as illustrated in FIG. 1.

Each pixel PX includes a switching transistor Qs, a driving transistorQd, a capacitor Cst and an organic light emitting diode LD.

The switching transistor Qs has a control terminal connected to one ofthe gate lines 121, an input terminal connected to one of the data lines171, and an output terminal connected to the driving transistor Qd. Theswitching transistor Qs transmits the data signals applied to the dataline 171 to the driving transistor Qd in response to a gate signalapplied to the gate line 121.

The driving transistor Qd has a control terminal connected to theswitching transistor Qs, an input terminal connected to the drivingvoltage line 172, and an output terminal connected to the organic lightemitting diode LD. The driving transistor Qd drives an output currentI_(LD) having a magnitude depending on the voltage between the controlterminal and the output terminal thereof, and outputs the output currentI_(LD) to the organic light emitting diode LD.

The capacitor Cst is connected between the control terminal and theinput terminal of the driving transistor Qd. The capacitor Cst stores adata signal applied to the control terminal of the driving transistor Qdand maintains the data signal after the switching transistor Qs turnsoff.

The organic light emitting diode LD has an anode connected to the outputterminal of the driving transistor Qd and a cathode connected to acommon voltage Vss. The organic light emitting diode LD emits lighthaving an intensity depending on the output current I_(LD) of thedriving transistor Qd, thereby displaying images.

The switching transistor Qs and the driving transistor Qd are n-channelfield effect transistors (“FETs”). However, at least one of theswitching transistor Qs and the driving transistor Qd may be a p-channelFET. In addition, the connections among the transistors Qs and Qd, thecapacitor Cst, and the organic light emitting diode LD may be modifiedin alternative exemplary embodiments.

Now, the structure of the OLED display will be described in furtherdetail with reference to FIGS. 2 and 3 along with FIG. 1.

FIG. 2 is a schematic diagram showing an arrangement of a plurality ofpixels in the OLED display according to an exemplary embodiment of thepresent invention. FIG. 3 is a cross-sectional view showing fourneighboring pixels in the OLED display shown in FIG. 2.

Referring to FIG. 2, the OLED display according to an exemplaryembodiment of the present invention includes red pixels R for displayinga red color, green pixels G for displaying a green color, blue pixels Bfor displaying a blue color and white pixels W for displaying a whitecolor, which are sequentially and alternately disposed. The red pixelsR, the green pixels G and the blue pixels B are basic pixels to displayfull colors, and the white pixels W are included to improve theluminance.

Four pixels of a red pixel R, a green pixel G, a blue pixel B and awhite pixel W form one group, and may be repeatedly arranged accordingto rows and/or columns. However, the arrangement and the shape of thepixels may be variously changed in alternative exemplary embodiments.

Next, a more detailed structure of the OLED display of FIG. 2 will bedescribed with reference to FIG. 3.

In FIG. 3, one pixel group indicated by the dotted line of FIG. 2 andincluding a red pixel R, a green pixel G, a blue pixel B and a whitepixel W in the OLED display shown in FIG. 2 is represented.

A plurality of thin film transistor arrays are arranged on an insulatingsubstrate 110. The thin film transistor arrays include switching thinfilm transistors Qs and driving thin film transistors Qd which aredisposed and electrically connected in each pixel.

A lower insulating layer 112 is formed on the thin film transistorarrays.

Red filters 230R, green filters 230G and blue filters 230B are formed inthe red pixels, green pixels and blue pixels, respectively, on the lowerinsulating layer 112, and a color filter may not be formed ortransparent filters (not shown) may be formed in the white pixels W. Thecolor filters 230R, 230G and 230B may be disposed as a color filter onarray (“CoA”) type.

An upper insulating layer 180 is formed on the color filters 230R, 230Gand 230B, and a translucent member 192 is formed on the insulating layer180. The translucent member 192 is made of a material havingcharacteristics such that a portion of light is transmitted and aportion of light is reflected. For example, the translucent member 193may be formed of an opaque conductor having a low absorption ratio suchas aluminum (Al) or silver (Ag) with a thickness of about 10 Å to about100 Å. The translucent member 192 is not present in the white pixels W.

The translucent member 192 simultaneously functions as an anodeelectrode.

A plurality of transparent members 193 are formed on the translucentmember 192 and the upper insulating layer 180, and the transparentmembers 193 are only arranged on some of the pixels and are not presenton other pixels. In the present exemplary embodiment, the transparentmembers 193 are only disposed on the green pixels G and the white pixelsW, and are not present on the red pixels R and the blue pixels B. Thetransparent members 193 disposed on the white pixels W function as theanode electrode.

The transparent members 193 may be made of a transparent conductor suchas ITO or IZO.

A plurality of organic light emitting members are formed on thetranslucent member 192 and the transparent member 193.

The organic light emitting members may include an auxiliary layer (notshown) for improving light emitting efficiency of a light emission layer370 as well as the light emission layer 370 for emitting light.

The emission layer 370 may include a plurality of sequentially depositedsub-emission layers emitting red, green and blue light, respectively,and may emit white light by combining the wavelengths of the red, greenand blue light. Herein, the present invention is not limited tovertically forming the sub-emission layers, as the sub-emission layersmay be horizontally formed. Also, the combination of light to emit thewhite light is not limited to red, green and blue color light. Thesub-emission layers may be formed with various color combinations thatemit the white light.

In addition, the auxiliary layer may include at least one selected froman electron transport layer (not shown), a hole transport layer (notshown), an electron injecting layer (not shown) and a hole injectinglayer (not shown).

A common electrode 270 is formed on the organic light emitting members.In exemplary embodiments, the common electrode 270 is made of a materialwith a high reflection rate, and functions as a cathode electrode. Thecommon electrode 270 is formed to cover the whole surface of thesubstrate 110, and forms a pair of electrodes with each translucentmember 192 or transparent member 193 which function as the anodeelectrode to flow the current to the organic light emitting members 370.

In an exemplary embodiment of the present invention, the translucentmember 192 generates a micro-cavity effect along with the commonelectrode 270. The micro-cavity effect occurs when light is repeatedlyreflected between a reflection layer and translucent layers, which arespaced from each other by an optical path length such that light of apredetermined wavelength is enhanced by constructive interference. Here,the common electrode 270 functions as the reflection layer, and thetranslucent member 193 functions as the translucent layers.

The common electrode 270 modifies the light emitting characteristics ofthe light from the light emission layers 370, and light near awavelength corresponding to the resonance wavelength of the micro-cavityamong the modified light is enhanced through the translucent member 193while light of different wavelengths is suppressed.

Here, the enhancement and the suppression of the predeterminedwavelength may be determined according to the optical path length. Theoptical path length must satisfy the constructive interference conditionfor each wavelength according to the corresponding red, green and bluepixels.

Optical path lengths of at least two pixels among the red pixel R, theblue pixel B and the green pixel G are the same in an exemplaryembodiment of the present invention.

For example, as shown in FIG. 3, the optical path lengths L₁ of the redpixel R and the blue pixel B are the same, and the optical path lengthsL₁ may be determined as a value that simultaneously satisfies theconstructive interference condition in the wavelength of the red regionand the wavelength of the blue region, respectively.

The optical path length L₁ which simultaneously satisfies theconstructive interference condition in the red pixel R and the bluepixel B may be represented as in Equation 1.L ₁ ≈mλ ₁/2≈(m+1)λ₂/2  (1)

Here, m is a natural number, λ₁ is a wavelength of the red region, andλ₂ is a wavelength of the blue region. For example, it may be that m=1.

Optical path lengths of at least two pixels among the red pixel R, theblue pixel B and the green pixel G are the same such that the processesrequired for forming the different optical path lengths for each pixelmay be reduced. That is, to form the different optical path lengths foreach pixel, at least three photolithography processes to form thedifferent thicknesses of the transparent members 193 disposed in eachpixel are required or the emitting materials are respectively depositedin each pixel by using shadow masks to form the different thicknesses ofthe organic light emitting members including the emission layers 370.However, optical path lengths of at least two pixels among the red pixelR, the blue pixel B and the green pixel G are the same such that thenumber of required processes may be reduced.

On the other hand, the optical path length L₂ of the green pixel G isdifferent from the optical path lengths L₁ of the red pixel R and theblue pixel B. That is, the optical path length L₂ of the green pixel Gmay be less than or more than the optical path lengths L₁ of the redpixel R and the blue pixel B. In FIG. 3, the optical path length L₂ ofthe green pixel G is more than the optical path lengths L₁ of the redpixel R and the blue pixel B.

When the optical path length L₂ of the green pixel G is more than theoptical path lengths L₁ of the red pixel R and the blue pixel B, theoptical path length L₂ of the green pixel G may be represented as inEquation 2.L ₂≈(m+1)λ₃/2  (2)

Here, m is a natural number and λ₃ is a wavelength of the green region.

Conversely, when the optical path length L₂ of the green pixel G is lessthan the optical path lengths L₁ of the red pixel R and the blue pixelB, the optical path length L₂ of the green pixel G may be represented asin Equation 3.L ₂ ≈mλ ₃/2  (3)

Here, m is a natural number and λ₃ is a wavelength of the green region.

This optical path length may be controlled by the transparent member193. In FIG. 3, the green pixel G has the transparent member 193 on thetranslucent member 192, and thus has a longer optical path length L₂. Incontrast, the red pixel R and the blue pixel do not have the transparentmember 193 and thus they have shorter optical path lengths L₁.

Because the white pixel W does not form the micro-cavity, it is notnecessary to additionally control the optical path length thereof.

FIG. 4 is a cross-sectional view of an OLED display according to anotherexemplary embodiment of the present invention.

Referring to FIG. 4, most of the constituent elements of the presentexemplary embodiment are the same as those of the OLED display shown inFIG. 3, but the optical path lengths L₂ of the green pixel G and theblue pixel B are the same, and the optical path length L₁ of the redpixel R is different, contrary to the previously described exemplaryembodiment.

The optical path length L₁ of the red pixel R may be less than or morethan the optical path length L₂ of the green pixel G and the blue pixelB. FIG. 4 represents the case in which the optical path length L₁ of thered pixel R is less than the optical path length L₂ of the green pixel Gand the blue pixel B.

The optical path length L₁ of the red pixel R may be represented as inEquation 4.L ₁ ≈mλ ₁/2  (4)

Here, m is a natural number and λ₁ is a wavelength of the red region.

For example, it may be that m=1.

The optical path lengths L₂ of the green pixel G and the blue pixel Bare determined as a value which simultaneously satisfies theconstructive interference condition in the wavelength of the greenregion and the wavelength of the blue region, and may be represented asin Equation 5.L ₂(m+1)λ₂/2≈(m+2)λ₃/2  (5)

Here, m is a natural number, λ₂ is a wavelength of the green region, andλ₃ is a wavelength of the blue region.

The optical path length may be controlled by the transparent member 193.The transparent members 193 are only formed in the green pixel G and theblue pixel B and are not present in the red pixel R, so that the greenpixel G and the blue pixel B have long optical path lengths and the redpixel R has a short optical path length. Because the white pixel W doesnot form the micro-cavity, it is not necessary to additionally controlthe optical path length thereof.

The emission characteristics of the OLED display according to theabove-described exemplary embodiment will be described in further detailwith reference to FIGS. 8 and 9.

FIG. 8 is a graph showing red, green, and blue light spectrums and awhite light spectrum in the OLED display according to the presentexemplary embodiment. FIG. 9 is a graph showing an increased ordecreased ratio of the intensity of the light spectrum by themicro-cavity in the graph shown in FIG. 8 compared with the intensity ofwhite light spectrum in the predetermined wavelength.

In FIGS. 8 and 9, “A” is a light spectrum of the micro-cavity conditionaccording to the first exemplary embodiment as in FIG. 3, that is, inthe case in which the optical path lengths of the red pixel R and theblue pixel B are the same, the peaks appear at the red wavelength regionat about 610 nm and at the blue wavelength region at about 460 nm.

“B” is a light spectrum of the micro-cavity condition according to thesecond exemplary embodiment as in FIG. 4, that is, in the case in whichthe optical path lengths of the green pixel G and the blue pixel B arethe same, and the peaks appear at the green wavelength region at about540 nm and at the blue wavelength region at about 460 nm.

As shown in the graphs, although the optical path lengths are controlledto be the same in two pixels among the red pixel R, the green pixel Gand the blue pixel B, each pixel may display the red, green and bluepixels. Accordingly, the number of processes to form the differentoptical path lengths for each pixel may be reduced and the desired colormay be displayed.

FIG. 5 is a cross-sectional view of an OLED display according to yetanother exemplary embodiment of the present invention.

Referring to FIG. 5, most of the constituent elements of the presentexemplary embodiment are the same or almost the same as those of theOLED display shown in FIG. 3, but a transparent electrode 191 is formedunder a translucent member 192 in each pixel, different from theabove-described exemplary embodiment.

The transparent electrode 191 improves the adhesion between thetranslucent member 192 and the upper insulating layer 180. Particularly,the upper insulating layer 180 has contact holes (not shown) forconnecting the driving thin film transistor Qd to an anode electrode,and when the translucent member 192 is directly formed on the contactholes, the thin film transistor and the anode electrode may bedisconnected due to deterioration of the adhesion. The transparentelectrode 191 may eliminate or effectively reduce this deterioration ofthe adhesion.

Now, other alternative exemplary embodiments of the present inventionwill be described in further detail with reference to FIGS. 6 and 7.

FIGS. 6 and 7 are cross-sectional views of OLED displays according toother alternative exemplary embodiments of the present invention.

In FIGS. 6 and 7, like the above-described exemplary embodiment, OLEDdisplays include red pixels R, green pixels G, blue pixels B and whitepixels W, and each pixel includes a switching thin film transistor Qsand a driving thin film transistor Qd which are electrically connectedto each other.

A lower insulating layer 112 preferably made of silicon nitride isformed on the switching thin film transistor Qs and the driving thinfilm transistor Qd, and a red filter 230R, a green filter 230G and ablue filter 230B are formed in a red pixel R, a green pixel G and a bluepixel B, respectively, on the lower insulating layer 112.

An upper insulating layer 180 preferably made of an organic material isformed on the color filters 230R, 230G and 230B. The upper insulatinglayer 180 is not present in the white pixel W.

A translucent member 192 is formed on the upper insulating layer 180 andthe lower insulating layer 112. The translucent member 192 hascharacteristics such that a portion of light is transmitted and aportion of light is reflected, and uses distributed Bragg reflection(“DBR”) for controlling the reflection ratio of the specific wavelength.

The translucent member 192 includes a plurality of layers which arealternately deposited. In exemplary embodiments, the plurality of layersare made of inorganic materials having different refractive indexes.When the translucent member 192 is made of inorganic materials with aplurality of layers, a loss of light may be reduced under thetransmitting or the reflection of the light compared with using a metal.

As shown FIGS. 6 and 7, the translucent member 192 includes a lowerlayer 192 p, a middle layer 192 q and an upper layer 192 r.

In FIG. 6, the upper layer 192 r is not present in the red pixel R andthe blue pixel B, and the upper layer 192 r is not present in greenpixel G in FIG. 7. This is to control the optical path length in the redpixel R, the green pixel G and the blue pixel B, and will be describedlater.

The three-layered structure is represented in FIGS. 6 and 7, but thepresent invention is not limited thereto and the lower layer 192 p andthe upper layer 192 q may be alternately deposited.

Here, the lower layer 192 p and the upper layer 192 r are made of thesame material having a first refractive index, and the middle layer 192q is made of a material having a second refractive index. For example,the lower 192 p and the upper layer 192 r may be made of silicon nitrideSiN_(x) having a refractive index of about 1.8, and the middle layer 192q may be made of silicon oxide SiO₂ having a refractive index of about1.5, but is not limited thereto.

A pixel electrode 191 is formed on the translucent member 192, and anemission layer 370 and a common electrode 270 are formed on the pixelelectrode 191.

In the present exemplary embodiment, like the above-described exemplaryembodiment, the optical path lengths of at least two pixels among thered pixel R, the blue pixel B and the green pixel G are the same. Here,the optical path length may be controlled by the upper layer 192 r.

As shown in FIGS. 6 and 7, the optical path lengths L₁ of the red pixelR and the blue pixel B are the same in the present exemplary embodiment.The optical path length L₁ is determined as a value which simultaneouslysatisfies the constructive interference condition in the wavelengths ofthe red region and the blue region, and may be represented as inEquation 6.L ₁ ≈mλ ₁/2≈(m+1)λ₂/2  (6)

Here, m is a natural number, λ₁ is a wavelength of the red region, andλ₂ is a wavelength of the blue region.

The optical path length L₂ of the green pixel G may be more than or lessthan the optical path lengths L₁ of the red pixel R and the blue pixelB. In FIG. 6, the optical path length L₂ of the green pixel G is morethan the optical path lengths L₁ of the red pixel R and the blue pixelB. In FIG. 7, the optical path length L₂ of the green pixel G is lessthan the optical path lengths L₁ of the red pixel R and the blue pixelB.

In FIG. 6, when the optical path length L₂ of the green pixel G is morethan the optical path lengths L₁ of the red pixel R and the blue pixelB, the optical path length L₂ of the green pixel G may be represented asin Equation 7.L ₂≈(m+1)λ₃/2  (7)

Here, m is a natural number and λ₃ is a wavelength of the green region.

In this case, because the upper layer 192 r is only formed in the greenpixel G in FIG. 6 and is not present in the red pixel R and the bluepixel B, the thickness of the upper layer 192 p may control the opticalpath length L₂ of the green pixel G.

Conversely, as shown in FIG. 7, when the optical path length L₂ of thegreen pixel G is less than the optical path lengths L₁ of the red pixelR and the blue pixel B, the optical path length L₂ of the green pixel Gmay be represented as in Equation 8.L ₂ ≈mλ ₃/2  (8)

Here, m is a natural number and λ₃ is a wavelength of the green region.

Here, because the upper layer 192 r is only formed in the red pixel Rand the blue pixel B and is not present in the green pixel G, thethickness of the upper layer 192 r may control the optical path lengthsL₁ of the red pixel R and the blue pixel B.

On the other hand, because the white pixel W includes the visible raysof all wavelengths, the micro-cavity amplifying the predeterminedwavelength is not formed thereto.

In an exemplary embodiment of the present invention, the upperinsulating layer 180 is removed in the white pixel W to remove themicro-cavity in the white pixel W. Accordingly, because the lower layer192 p made of silicon nitride is directly formed on the lower insulatinglayer 112 made of silicon nitride, the difference of the refractiveindex therebetween is not present such that the reflection and theinterference are not generated. Also, because the upper layer 192 r isalso removed, the middle layer 192 q is made of silicon oxide such thatthe micro-cavity may not be formed. Accordingly, the white light emittedfrom the emission layer 370 is not affected by a micro-cavity in thewhite pixel W and is emitted as it is.

In the present exemplary embodiment, the upper layer 192 r in a portionof the pixels is removed such that the optical path length may becontrolled. Because the removal of the upper layer 192 r requires onephotolithography process, the process may be simplified in comparisonwith the several photolithography processes to form the differentoptical path lengths in the red pixel R, the blue pixel B and the greenpixel G.

On the other hand, because the lower layer 192 p, the middle layer 192 qand the upper layer 192 r are formed on the upper insulating layer 180made of an organic material, it is preferable that they are formed bychemical vapor deposition (“CVD”) at a relatively low temperature ofless than about 200° C. Also, as above-described, silicon nitride,silicon oxide and silicon nitride are sequentially deposited to form thelower layer 192 p, the middle layer 192 q and the upper layer 192 r, andwhen etching the silicon nitride an etch gas including CF₄ and O₂ isused and when etching the silicon oxide an etch gas including C₄F₈ andH₂ is used, for etch selectivity between the silicon nitride and thesilicon oxide.

In the present exemplary embodiment, the optical path lengths of the redpixel R and the blue pixel B are the same and the optical path length ofthe green pixel G is different therefrom, but the present invention isnot limited thereto, and it may be determined that the optical pathlengths of at least two pixels among the red pixel R, the green pixel Gand the blue pixel B are the same.

In the above-described exemplary embodiments, the emission layer 370emits the white light, but this is not limiting, and a structureincluding a red emission layer, a green emission layer and a blueemission layer respectively formed in the red pixel R, the green pixel Gand the blue pixel B may be identically adapted, and the color filters230R, 230G and 230B disposed in each corresponding pixel may be omitted.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosed exemplaryembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. An organic light emitting diode (OLED) display comprising a firstpixel, a second pixel and a third pixel displaying different colors fromeach other, the OLED display comprises: a substrate; a reflectingelectrode on the substrate; and a translucent member forming amicro-cavity along with the reflecting electrode, wherein an opticalpath length is a gap between the reflecting electrode and thetranslucent member, wherein the first pixel is a green pixel, the secondpixel is a blue pixel, and the third pixel is a red pixel, whereinoptical path lengths of the first pixel and the second pixel are thesame, and wherein the optical path length of the first pixel is greaterthan an optical path length of the third pixel.
 2. The OLED display ofclaim 1, further comprising a transparent member disposed between thereflecting electrode and the translucent member, and the transparentmember is formed in a portion of at least one pixel among the firstpixel, the second pixel and the third pixel.
 3. The OLED display ofclaim 2, wherein the translucent member includes silver or aluminum, andthe transparent member includes ITO or IZO.
 4. The OLED display of claim2, wherein the transparent member is formed in the first pixel thesecond pixel and not in the third pixel.
 5. The OLED display of claim 1,wherein the optical path length L2 of the third pixel satisfies L2≈mλ3/2and the optical path length L1 of the first pixel and the second pixelsatisfies L1≈(m+1)λ1/2≈(m+2)λ2/2, where m is a natural number, λ1 is awavelength of the green region, λ2 is a wavelength of the blue region,and λ3 is a wavelength of the red region.
 6. The OLED display of claim1, further comprising a white pixel, wherein the translucent member isabsent in the white pixel.
 7. The OLED display of claim 1, wherein thefirst pixel, the second pixel and the third pixel include acorresponding color filter.
 8. The OLED display of claim 7, furthercomprising an emission layer disposed between the reflecting electrodeand the translucent member, and the emission layer includes a pluralityof sub-emission layers emitting light of different wavelengths and emitsa white light by combining the light of the different wavelengths.